Heart Anatomy

Heart Anatomy


  • Snugly enclosed within the middle mediastinum (medial cavity of the thorax)
    • Contains the heart, pericardium, vessels to & from the heart & lungs, trachea & esophagus.
    • M.Mediastinum – located in the inferior mediastinum (lower than the sterna angle)
  • Extends obliquely from 2nd rib à 5th intercostals space.
  • Anterior to Vertebrae
  • Posterior to Sternum
  • Flanked by 2 lungs
  • Rests on the diaphragm
  • 2/3 of its mass lies to the LHS of the midsternal line.

The Pericardium: (Coverings of the Heart)

  • A double-walled sac
  • contains a film of lubricating serous fluid
  • 2 Layers of Pericardium:

Fibrous Pericardium:

  • Tough, dense connective tissue
  • Protects the heart
  • Anchors it to surrounding structures
  • Prevents overfilling of the heart – if fluid builds up in the pericardial cavity, it can
  • inhibit effective pumping. (Cardiac Tamponade)

Serous Pericardium: (one continuous sheet with ‘2 layers’)

  • Parietal Layer – Lines the internal surface of the fibrous pericardium
  • Visceral Layer – (aka Epicardium) Lines the external heart surface

Layers of the Heart Wall:


  • Visceral layer of serous pericardium


  • Muscle of the heart
  • The layer that ‘contracts


  • Lines the chambers of the heart
  • Prevents clotting of blood within the heart
  • Forms a barrier between the O2 hungry myocardium and the blood. (blood is supplied via the coronary system)

Fibrous Skeleton of the Heart

  • The network of connective tissue fibers (collagen & elastin) within the myocardium
  • Anchors the cardiac muscle fibers.
  • Reinforces the myocardium

2 Parts


  • Flat sheets separate atriums, ventricles & left and right sides of the heart.
  • Electrically isolates the left & right sides of the heart (conn. Tissue = non-conductive)
    • Important for cardiac cycle
  • (interatrial septum/atrioventricular septum/interventricular septum)


  • Rings around great vessel entrances & valves
  • stop stretching under pressure

Chambers & Associated Great Vessels

2 Atrias (superior): [Atrium = Entryway]

  • Thin-walled Receiving Chambers
  • On the back & superior aspect of the heart.
  • Each has a small, protruding appendage called Auricles – increase atrial volume.
  • Septal Area
    • Connective tissue dividing L & R atria. (Site of Foetal Shunt Foramen ovale)
  • Right Atrium:
    • Smooth internal posterior wall
    • Where veins drain into (either from body/lungs)
    • Ridged internal anterior wall – due to muscle bundles called Pectinate Muscles.
    • Blood enters via 3 veins:
    • Superior Vena Cava
    • Inferior Vena Cava
    • Coronary Sinus (collects blood draining from the myocardium)
  • Left Atrium:
    • Smooth internal post. & ante. walls.
    • Blood enters via:
      • The 4 pulmonary veins (O2 blood) [Pulmonos = Lung]

2 Ventricles (inferior): [Vent = Underside]

  • Thick, muscular Discharging Chambers
  • The ‘pumps’ of the heart
  • Trabeculae Carnea [crossbars of flesh] line the internal walls
  • Papillary Muscles play a role in valve function.
  • Right Ventricle:
    • Most of the heart’s Anterior Surface
    • Thinner – responsible for the Pulmonary Circulation – Via Pulmonary Trunk
  • Left Ventricle:
    • Thicker – it is responsible for the Systemic Circulation – Via Aorta
    • Most of the heart’s PosteroInferior Surface

Landmarks of the Heart:

  • Coronary Sulcus (Atrioventricular Groove):
    • Encircles the junction between the Atria & Ventricles like a ‘Crown’ (Corona).
    • Cradles the Coronary Arteries (R&L), Coronary Sinus, & Great Cardiac Vein
  • Anterior Interventricular Sulcus:
    • Cradles the Anterior Interventricular Artery
    • Separates the right & left Ventricles anteriorly
    • Continues as the posterior Interventricular Sulcus.
  • Posterior Interventricular Sulcus:
    • Continuation of the Anterior Interventricular Sulcus
    • Separates the right & left Ventricles posteriorly

Pathway of Blood Through the Heart:

The systemic and pulmonary circuits:

  • The right side of the heart pumps blood through the pulmonary circuit (to the lungs and back to the
  • the left side of the heart).
    • Blood flowing through the pulmonary circuit gains oxygen and loses carbon dioxide,
  • indicated by the color change from blue to red.
  • The left side of the heart pumps blood via the systemic circuit to all body tissues and back to the
  • the right side of the heart.
    • Blood flowing through the systemic circuit loses oxygen and picks up carbon dioxide (red to
  • blue color change)

Coronary Circulation

  • The myocardium’s own blood supply
  • The shortest circulation in the body
  • Arteries lie in the epicardium – prevents the contractions inhibiting blood flow
  • There is a lot of variation among different people.

Arterial Supply

  • Encircle the heart in the coronary sulcus
  • Aorta – Left & Right coronary arteries
    • Left Coronary Artery – 2 Branches:
      • 1. Anterior InterVentricular Artery (aka. Left Anterior Descending Artery …or LAD).
        • Follows the Anterior InterVentricular Sulcus
        • Supplies blood to InterVentricular Septum & Anterior walls of both Ventricles.
      • 2. Circumflex Artery
        • Follows the Coronary Sulcus (aka. AtrioVentricular Groove)
        • Supplies the Left Atrium & Posterior walls of the Left Ventricle
  • Right Coronary Artery – 2 (‘T-junction) Branches:
    • 1. Marginal Artery:
      • Serves the Myocardium Lateral RHS of Heart
    • 2. Posterior Interventricular Artery:
      • Supplies posterior ventricular walls
      • Anastomoses with the Anterior Interventricular Artery

Venous Drainage:

  • Venous blood – collected by the Cardiac Veins:
    • Great Cardiac Vein (in Anterior InterVentricular Sulcus)
    • Middle Cardiac Vein (in Posterior InterVentricular Sulcus)
    • Small Cardiac Vein (along Right inferior Margin)
      • – Which empties into the Right Atrium.

Heart Valves:

  • Ensure unidirectional flow of blood through the heart.
  • 2x AtrioVentricular (AV) (Cuspid) Valves:
    • Located at the 2 Atrial-Ventricular junctions
    • Prevent backflow into the Atria during Contraction of Ventricles
    • Attached to each valve flap are chordae tendinae (tendonous cords) “heart strings”
      • Anchor the cusps to the Papillary Muscles protruding from ventricular walls.
        • Papillary muscles contract before the ventricle to take up the slack in the chordae tendinae.
        • Prevent inversion of valves under ventricular contraction.
  • Right AV Valve:
    • The “Tricuspid Valve”
    • 3 flexible ‘cusps’ (flaps of endocardium + Conn. Tissue)
  • Left AV Valve:
    • The “Mitral Valve” or “Biscupid Valve”
    • (resembles the 2-sided bishop’s miter [hat])
  • 2x SemiLunar (SL) Valves:
    • Guard the bases of the large arteries issuing from the Ventricles.
    • Each consists of 3 pocket-like cusps resembling a crescent moon (semilunar = half moon)
    • Open under Ventricular Pressure
    • Pulmonary Valve:
      • Between Right Ventricle & Pulmonary Trunk
    • Aortic Valve:
      • Between Left Ventricle & Aorta

Valve Sounds:

  • 1. “Lubb”:
    • Sound of a Cuspid Valve closing
  • 2. “Dupp”:
    • Sound of a Semilunar Valve Closing
  • Where to Listen:

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